Re: [PATCH] libxl: force netback to wait for hotplug execution before connecting

[Julien Grall <julien@xxxxxxx>]

Hi Roger,

On 25/01/2022 16:09, Roger Pau Monné wrote:
> On Tue, Jan 25, 2022 at 03:32:16PM +0000, Julien Grall wrote:
> > Hi,
> >
> > On 24/01/2022 16:02, Roger Pau Monne wrote:
> > > By writing an empty "hotplug-status" xenstore node in the backend path
> > > libxl can force Linux netback to wait for hotplug script execution
> > > before proceeding to the 'connected' state.
> > I was actually chasing the same issue today :).
> >
> > > This is required so that netback doesn't skip state 2 (InitWait) and
> > Technically netback never skip state 2 (otherwise it would always be
> > reproducible). Instead, libxl may not be able to observe state 2 because
> > receive a watch is asynchronous and doesn't contain the value of the node.
> > So the backend may have moved to Connected before the state is read.
> Right, might be more accurate to say it skips waiting for hotplug
> script execution, and thus jumps from state 2 into 4.
I would add the jump happens when the frontend decides to connect.

> Note I think
> it's also possible that by the time we setup the watch in libxl the
> state has already been set to 4.
Correct.

Cheers,

--
Julien Grall